By traditional crops we mean those in which non-invented varieties, manual cultural practices and industrial inputs remain marginal, while the procedures are linked to oral traditions integrated into rural societies.
The matrices of all traditional crops have been forest or savanna tree gardens. Initially itinerant, they were later included in rotations of farming systems or in hut gardens that were not very mobile. This led to a shift from polycultural gardens with associated crops to more or less homogeneous soils of yam varieties.
But it is still necessary to respect the modalities of “picking” still alive in many regions. They can be directed to edible native species, but not cultivated. These have become exceptional in the West Indies for the “bamboche or ouaoua yams” (which are not Dioscorea but Rajania cordata, an American Dioscorea, quite common in forests, especially on the edges and in clearings), but they are still practiced in Africa, Melanesia and Asia for various Dioscorea species and species close to the cultivated complex, D. cayenensis-rotundata, such as D. prahaensilis or even D. mangenotianajeune. The Pygmies of Central Africa have developed a bamboo auger capable of extracting tubers from great depths. It is also sometimes a question of cultivars escaped from cultivation and propagated by their bulbils, D. bulbifera in Ivory Coast, D. nummularia in New Caledonia or D. hispida in the Philippines are examples, as well as D. alata whose forms called in the West Indies “Wild”, “En bas-bon”, “Bocodji” etc. are not rare in the young secondary forests and gallery forests of the waterways Traditionally, only the lower two-thirds or three-quarters of the trees are removed, the very lignified “head” being left in place (“En bas-bon”!).
2.1 – Cultural succession
Yam cropping systems fall within the full range of succession types.
In shifting cultivation, practiced in almost all the humid tropical zone, yam is very competent. It is so in tropical America where the “cara” in Brazil, the “napi” in Guyana (D. trifida) intervenes in the abattis, clearing cultivated on slash and burn one or two years in the primary or secondary forest. In its initial form, the return to former clearings was infrequent. With the reduction of migration and the reduction of primary forest areas, it tends to be located in a less and less defined area. Population growth is undoubtedly responsible, particularly in Haiti, for the shift to forest fallows, then shrublands. In the 1980s, twenty-year forest fallows were still known in the hinterland of Jérémie, beyond Chambellan.
In Burma, the “taungya” system includes an agricultural phase at the beginning of each forest plantation cycle, which may include yams. However, it is more common everywhere for simple coppice and herbaceous rangeland to be recovered periodically. In addition to the duration of the fallow, the nature of the vegetation stand before its recovery makes it possible to evaluate the degree of fertility restoration.
Generally, yam is the main crop, alone or in combination. The following successions can be justified:
| Yam: 4 years alone then Yam + Potato + Peanut or Corn: 3 years | Anambra |
| Herbaceous fallow : 2 years | Nigeria |
| Yam-based culture: one to three years | Lakoja |
| Fallow: one to three years | (Nigeria) |
| Yam: two to three years | Little Town |
| Fallow land: less than three years | (Guadeloupe) |
However, in areas of the Lesser Antilles, where banana or sugarcane predominate, yam and its associative procession may follow the farm crop. In Barbados, sugarcane is sometimes planted as a late intercrop with yam ridges. In fact, this system is a replica of the “taungya” systems, with the return of yam after a number of “offshoots” of cane, formerly seven to ten years and beyond, now much reduced.
2.2 – Yam-based cultural associations
In addition to the above case, yam is found in association with a considerable variety of plants. The most famous are the food Araceae, Asiatic-Polynesian taro (Colocasia esculenta) or American “taro” (Xanthosoma sagittifolia). With cereals and especially corn, these associations are also common.
The study of mixed farming in the West Indies and French Guiana has shown forms of organization of decreasing complexity from the home garden to the exclusively commercial plot.
In the case garden, the yams themselves will be very diverse (several varieties, several species), planted and characterized over a long period, sometimes with fruit trees as stakes, and without strict alignments. Table V gives an example of sequences presented in Guadeloupe.
2.3 – Traditional crops with homogeneous and intensive tendencies
These crops have already been described in certain ancient contexts, such as the ceremonial or competition yam crops of the Pacific islands (New Guinea, New Caledonia…). Their development has increased with that of the market economy.
They can be broken down as follows:
1. More or less homogeneous crops, in patches of variable size within a polycultural garden. This is often the case, for example, in gardens in the Mana region of Guyana with “Indian yam” (D. trifida). These patches may or may not be staked (gardens with D. alata recently introduced in Guadeloupe), and may be better tended or, conversely, less tended than the plants left in the associative set. The varietal selection is reduced to one or two cultivars.
2. More or less homogeneous crops, constituting the main part of the garden or a totally distinct sole. They become the majority and are distinguished from modernized crops only by the overall weakness of the inputs, of which only one (or very few) of the possible elements are used. Thus frequently in Jamaica and Nigeria: with one to three cultivars of D. rotundata, at most, preparation, maintenance and harvesting will remain manual, but fertilization will be trivial, the crop always being tutored. These gardens can be several hectares in size. In the Lesser Antilles (Barbados, French Antilles), mechanical preparation of the land in ridges is general. Staking is rarely practiced (L. alata, more rarely D. rotundata). Pesticides are sometimes used, but harvesting is only done manually.
(introduction)
Through the practices of traditional cultures, we can discern a large amount of knowledge that we will try to order because of their agronomic relevance.
2.4.1 – Importance of soil organic matter content
We have already mentioned the duration and the nature of the people of the fallows and the precedents, such as the Cane and the Banana tree, which ensure a balanced restoration of the fertility. To this must be added the direct contributions made during the tillage of the soil. In addition to manure and weeding waste, we can mention bagasse and skimmings, by-products of sugar production, which can represent up to 80 t/ha in Guadeloupe.
2.4.2 – Mechanical tillage
Even when work and ridging are done mechanically, as in the Lesser Antilles, the traditional planter loosens the ridges with a fork. The texture of the soil must be as fine as possible, especially in the zone of growth of the tuber. It is obtained by making mounds, accompanied or not by a “pit” of about 80-100 cm x 50-70 cm. The stones are excluded if possible. Sometimes, the spreading of the extracted soil on the surface preserves the succession of horizons for a few days. The incorporation of organic elements is often appreciated by practitioners as much for its textural as for its nutritional virtues. In deep yam pits, palm gains or other plant material are used to support the soil.
The mounds can be individual and even, as in Jamaica, extended by ridges or other anti-erosion devices, or built in continuity to a simulated ridge. Their height and volume vary with the soil, particularly according to the proximity of the water table. They can reach 1.50 m high and 2 m in diameter.
2.4.3 – Varietal characteristics
Although it has been greatly reduced, knowledge of varieties is an essential basis of traditional culture. The main points of support can be summarized as follows.
2.4.3.1- Culinary properties
The traditional farmer is always, with his family, a big consumer of yam and therefore takes into account the apparent food characteristics of the varieties. The color of the chair to the cooking, shade and homogeneity is the first. Then come, almost equally, the taste and texture. These three major elements on which the speed and mode of cooking (peeled or not, roasted, boiled or fried, in water or steam) play, determine the preferences. These preferences vary according to country, ethnicity and yam species. Thus, in D. trifida, medium purple chairs are generally preferred, in D. cayenensis-rotundata we know preferences for a certain bitterness of yellow yam and for its opposite, in D. cayenensis-rotundata preferences for a dry or pasty texture, without forgetting technological aptitudes such as those for West African “foufou”.
2.4.3.2 – Cultural particularities
The first is the ability of the plant. Some varieties are given as more easily propagated, either from the head alone, or from any part of the single harvest tuber or regeneration tuber. In the latter case, the technique of cutting the tuber requires some attention, because of the zones of stem departure that its morphology favors (fig. 3): it is advantageous to privilege certain areas by a pruning where the farmer’s know-how is exercised. The aptitude for the production of bulblets is obviously taken into account.
Staking generates a surplus of production, compared to flat cultivation, which varies from about 10% to 100% depending on the species, variety, ecology, fertilization, height and earliness of staking. D. cayenensis-rotundata is more demanding in this respect than D. alata. But if in rainy regions, staked, the first one escapes better to Rhizoctonia solani, the second one is also less affected by anthracnose. The economic profitability of the usual production surplus may be cancelled by the cost of staking and harvesting (accumulated extraction time for more irregular tubers), by the shrinking market for the large tuber and by losses related to lesions and breakage more numerous. D. trifida and D. dumetorum value staking less.
The earliness of the foliage installation, the relative importance of this one and its duration count. They determine the possibilities of associating different varieties or species on the same mound or on the same stake. Thus, on the same mound, one can find a long-cycle D. cayenensis-rotundata (Yellow Yam), an early D. alata (cv St-Vincent) and a D. bulbifera even earlier in its aerial production. These same characteristics will also intervene, with others, in the establishment of associated species, other than yams.
The time of maturity and its flexibility of use (see below on cycle management) combine with the productivity of the variety. If D. alata are generally recognized as more productive (in the absence of parasitism) their maturity seems to be more related to short days (September to February in the northern hemisphere) than that of D. cayenensis-rotundata.
2.4.3.3 – Commercial value
The previous data on maturity is already part of it.
The average weight of the tuber is an important element but it is relativized by the species, the country and the type of market selected. The optimum expected for a D. trifida or D. esculenta will be of the order of a few hundred grams, but several kilos for D. alata and D. cayenensis-rotundata in the West Indies, on rural markets. For the latter, in large-scale markets, and especially for export, the optimum will be around one kilo. The general trend towards weight reduction can be met more by cultural management than by variety. The same is true, although to a lesser degree, for shape, another commercial element (Fig. 18). This management can also partly correct certain varietal defects concerning the appearance of the bark: excessively rough and tormented, the bark of very productive bulbous varieties with a long cycle (“Taîti” from Guadeloupe, “Pyramid” from India) becomes much less so with a late plantation. The excess of rootlets, sometimes abundant in D. alata cvBelep, is reduced by a culture in well drained soil with perfect harvest at maturity. Early harvesting of D. alata cv ” Kinabayo ” and cv ” Oriental ” avoids the too frequent development of cracks at the lower tip…
2.4.4 – Managing the cultural cycle
Many traditional interventions refer to an astral calendar where the moon plays a universal role. The solstices and equinoxes are taken into account to varying degrees. In New Caledonia, at least fifteen years ago, the positions of the constellations were important for the launching of the campaign. In Guadeloupe, the summer solstices (St. John’s Day) are a reference as well as the lunar phases. The variations in tuber shape expected at certain planting times are sometimes related to these.
Some planters also know how to modify the distribution of the reserves granted to the underground tubers and bulbils by risking to run to the ground variable portions of lianas (“St-Vincent”, “Igname d’eau”, in Martinique).
One practice, which has been used in various ways, consists of seeking a cycle shift within the same varietal origin. This can be achieved by forcing plants to a higher temperature and humidity during dormancy (D. cayenensis-rotundata in Martinique), by early planting under irrigation, or by taking advantage of natural heterogeneity of emergence. In this last case, each year, a real physiological drift is thus identified and reinforced by massal selection. This procedure allows Jamaican yellow yam growers to carry out up to seven staggered plantings during the year, thus ensuring continuous export availability.
2.4.5 – Pest control
Prolonged exposure of the surface of the extracted soil, during the preparation of the pits, is given as a practice to fight against “worms” (white worms, nematodes?..). It is sometimes completed in Haiti, where the ravages of white worms (marocas) are worrying, by the burial of leaves, including those of the “nim” (Azadirachta indica). In the north of Haiti, the plantation within mounds of “fatras” (collection of leaves and debris in the coffee undergrowth) also protected against marocas. Elsewhere, it is mainly lime and ash that are used against white grubs. Ash is used everywhere against infections of the tuber after applying wounds or sectioning in fractional consumption. In vegetation, some practitioners use associations of tolerant and sensitive varieties to limit the effects of anthracnose. Some also take into account the lesser appetence of D. cayenensis-rotundata for defoliating ants (cassava ant (Acromyrmex octospinosus) in Guadeloupe and other Attines in Trinidad and in tropical and subtropical America.
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